Process for accelerating rubber vulcanization and compound therefor



Patented Apr, 5, '1932 UNITED" STATES .PATENT OFFICE HAROLD A. MORTON, or AKRON,- OHIO PROCESS FOR' ACGELERATING,RUBBER VULCANIZATION AND COMPOUND THEREFOR No Drawing. Application filed July 23,

invention relates to the art of manufacturing vulcanized rubber compositions and in particular to a process including as a step the incorporation in a rubbercompound theuse of materials which, may be termed as bivalent metallic salts containing two different acidic radicals, for accelerating the vulcanization action and to a rubber compound or composition having such an ac- 4 celerating substance incorporated therein.

Bivalentmetallic salts containing two identical acidic radicals-(e. g., zinc dimethyl dition to providea 'newclassfof materials which thio carbamat e)lhave heretofore been known to the prior artbut these materials in general have the disadvantage that they possess vundesirable characteristics, such as low"crit ical temperature, that *is, danger of iprevulcanization, high'cost,l

g offlexibility, etc;

It is, accordingly, a objectzofthis inven-' have the property of accelerating'vulcani'za- -tion and-imparting to the rubber: desirable pose at hand. I iglf lher'e are a great number of materials "which fall within the'scope ofthis invention characteristics, :Another object ofithis invention is to provide materials which'are stable, less expensive, and in whichthe activity may be varied over a fairly wide range, by the proper choice ofthera'wmaterials. The activity and temperature-ofcure ofthe resulting accelerator is' dependent to a large extent, on

the vparticular raw. materials employed.

For this reason, this class of materials is a A very flexible one and the properties maybe modified considerably to fit the specific purand in general they may be represented the following simple representation:

where R R are both acidic groups but I in no case shall they be identical. R shall in all cases be a dithio carbamic acid radical 1930. Serial No. 470,226.

derived from a di alkyl amine, as for example: v I

Dimethyl dithio carbamic acid radical (C 3)2NCSS- Diethyl dithio carbakmic acid radical meanness- Dipropyl dithio carbamic acid radical (C H NCS S- I Dibutyl dithio carbamicacid radical (C Hb)2NCSs R218 a dithio carbamic acid radical derived from a cyclic or heterocyclic amine,

The use of alkyl or aryl dithio carbamates of metals has been known to the prior art but in all cases R and R were identical. For example, metallic salts of. dimethyl dithio carbamic acid were known but possessed undesirable characteristics such as tendency to cause prevulcanization, high cost, etc. The

metallic salts of aryl dithio carbamates also showed undesirable properties, such as,

. slightfactivity, lack of stability and flexibility, etc.,' and produced rubber articles having inferior tensile strengths.

The present type oifers a distinct improve 7 v m'ent over the dithio carbamates known to the prior art due to the activity, stability, flexi bility low cost, etc., of the materials.

They also result in vulcanized articles having high tensile strength and elongation, durability and abrasion and flexing resistance.

The materials of Type I may be represented more specifically by the constitution:

(Ru) gNCSS M SSCNRDRQ In other words, one nitrogen atom shall be attached to two alkyl hydrocarbon residues and the other nitrogen shall be attached to two aryl hydrocarbon residues or to one hydrogen atom and one aryl hydrocarbon residue or to one aryl and one alkyl hydrocarbon residue or to a piperidyl residue.

These compounds may be prepared by treating an equimolecular mixture of a secondary aliphatic amine and a cylic or heterocylic amine with carbon disulphide and caustic soda and then adding a solution of a soluble salt of the desired bivalent metal.

One of the preferred members of this type of compounds is lead phenyl dimethyl dithio carbamate, the chemical constitution probably being:

This material may be readily prepared by treating one mol (-81.5 grams) of dimethyl amine hydrochloride and one mol of aniline hydrochloride (129.5 grams) with four mols (160 grams) sodiumhydroxide and two mols (152 grams) of carbon disulphide. After the above named ingredients have reacted completely, a solution of one mol 331 grams) of lead nitrate is added, whereupon the lead salt of phenyl dimethyl dithio carbamate acid is precipitated. This material may be filtered and dried by any of the known methods and after pulverizing is ready for use.

While it is thought the reaction takes place in the above manner, I do not wish to be bound by any of the theories here given butdesire to be protected by Letters Patent on the materials as formed.

This type of metallic dithio carbamate includes the following:

Zinc phenyl dimethyl dithio carbamate Zinc ortho tolyl diethyl dithio carbamate Zinc para tolyl dimethyl dithio carbamate cHanNcss-zn-sscNuc HoH;- am

Zinc ethyl phenyl dimethyl dithio carbamate (CH NCSSZnSSCN(C H5)CoHn Zinc xylyl dimethyl dithio carbamate oHQnNcsszn-sscriricumcn Zinc piperidyl dimethyl dithio carbamate (CH NCSSZn-SSCNC H Zinc alpha naphthyl dimethyl dithio carbamate (CH NCSSZnSSCNHC H a1pha Zinc beta naphthyl dimethyl dithio carbamate This type of metallic dithio carbamate is superior to the metallic dithio carbamatesknown to the prior art. The activity and properties may be varied considerably by the proper choice of the two components.

The vulcanized product exhibits high tensile strengths, elongation and in general the characteristics are superior to the simple nietallic dithio carbamates.

- The invention may be practiced by the utilization of lead phenyl dimethyl dithio carbamate, the quantity of course being dependent upon the rubber compound in question. It will be found that a satisfactory product may be obtained by employing from 0.25% to 3.0% based on 100 parts of rubber. The

quantity to be employed for any particular compound or rate of cure, can be easily determined by one skilled in the art.

This type of accelerating materials can be employed for vulcanization at various temperatures, although the preferred method of curing is at temperatures corresponding to $330 pounds steam pressure (250 F.274

These materials, in general, function to their maximum extent when zinc oxide is present as an activator.

As examples of carrying out the invention by the use of materials of Type I, the following typical examples are given. It is not,

however, restricted to such specific examples as many modificat ons may be made;

bamate Emample 1 (cHmNcss-Pb-sscNHCuH in a rubber compound is illustrated by this example. The recipe of the rubber compound is as follows: Smoked sheets -1 Q. 55.3125

Lead phenyl dimethyl dithio carbamate 0.65

. 100.0 The above stock was compounded, mixed and press cured over a range of cures andthe tensile strength measured:

This example serves to illustrate the use of several vdiflFerent metallic salts of this type. The recipe is as follows:

Rubber 100 Zinc oxide 10 Sulphur 4 Accelerator 1 In the following table of results, the accelerae tors are as follows;

Stock A=1% lead para tolyl dimethyl dithio carba-mate' v I en ances-rb; sscundH.CH3-p stock B-=1%;,1aa,xy1y1 dimeth-yl dithio carbamate- 1 I omamcss Pb-ssoNHcHa(cH;)i

Stock C =1% zinc beta naphthyl dimethyl dithio carbamate (CHQ NCSS-ZiiSSCNHC lE1 beta The stocks were mixed and cured and the tensile strength determined, using a sheet of stock fi th inch inthickness;

Stock A Stock B 3 Stock (3-.

Cute I I Tensile Elong. Tensile Elong. Tensile Elong.

s'xars V 3680 100% 10:20:: v I 4035 760% 15'XZHL- 1785 870% V 1470 990% 3935 I 770% 201207;- 1 4010 720% 3160 790%: 3120 880% X m 3585 790% 3385 870% W! 20:? 3750 760% i 3370 850% Ewample 5 Illustrating the use of zinc phenyl dimethyl dithio carbamate [(CH NCSS-Zn-SSCNHC H5] in a pure gum stock of the following composition:

Rubber 100 Steanc 01d Zinc oxide 1O S l h 2 Carbon black 20.0 p i a'- fl "i;- Zi id 1 2 75. Inc P y y 1t 10 car Pine tar oil 3.5 mate 1 Tensile strength measurements over a range of cures showed the following results:

Cure Tensile Elongation 1x40#. 3290 1 880% 2'X40# 3850 870% 3x40zfi: 4375 850 5'x40#. 3610 p 780% 5x20# 3650 800% 10'x20# 4275 770% 15x20# 4070 710% 7 Type I I Where, in the formula R is aidithiorarbamic acid radical derived from a straight chain aliphatic amine substituted by one or more cyclic groups, or an aliphatic diamine whether substituted or unsubstituted.

One of the preferred members of this type is lead (beta anilino ethyl) phenyl dimethyl dithio carbamate, the chemical constitution probably being:

' :H 1 :'css-Pb-ssorucaal )en crnrusicon5 This material may be readily prepared by treating one mol of dimethyl amine hydrochloride and one mol of'1-2 di (phenyl amino) ethane hydrochloride with four'mols of sodium hydroxide and two mols of carbon disulphide. v 1

The reaction is carried outat 15 centigrade or below and vigorous agitation is maintained. After theseingredients have reacted completely, one mol of a soluble lead salt, such as lead, nitrate, is added whereupon e s ready for use. I

Other members of this group (Type II) whichmay be mentioned are:

Lead [(B ortho toluidino ethyl) o-tolyl] dimethyl dithio carbamate Lead [(B para poluidino ethyl) p-tolyl] dimethyl dithio carbamate (CH3) 2no'ss Pb SSCN camera CH CH NHC H CH 1 Lead [(B xylidino ethyl) xylyl] dimethyl dithio carbamate the lead salt is precipitated. -After filter- A ing, drying and pulverizing, the material Zinc [(B xylidino ethyl) xylyl] diethyl dithio carbamate Q There are many other materials of this type which function in this manner and the above members simply serve to indicate the scope of the invention.

As examples of carrying out the invention by the use of materials of Type II the fol- O lowing are given.

Example 4 Theuse of accelerators of this type is illustrated in this example The rubber stock has the following composition Rubber 100 Zinc oxide 10 Sulphur 4 Stearic acid 1 Accelerator 1 In the following table of results, the stocks contain the following accelerators:

Stock A: Lead [(B para toluidino ethyl) p-tolyl] dimethyl dithio carbamate.

(CH3) 2vcss -Pb sscmcurncn 011 cnavnc rncri Stock B Lead [(B anilino ethyl) p-tolyl] dimethyl dithio carbamate (CHQQNCSS -Pb sscN canons) cri 'cn ivnc n Stock C Zinc [(B aniline ethyl) phenyl] dimethyl dithio carbamate (CH3) guess Zn SSCN (are) cn crnru-icun Stock DzLead [(B xylidino ethyl) xylyl] dimethyl dithio carbamate Stock EzLead [(B anilino ethyl) phenyl] dimethyl dithio carbamate (CH NCSS Pb SSCN C H CH CH NHC H The above stocks were mixed and cured and the tensile strength determined. These are given, for a range of cures, in the following table.

The above results demonstrate the wide range. of curing characteristics exhibited by members of this type of materials.

Type III Where, in the formula R1-M-R2 R is a radical containing the carboxyl acid group.

The materials of Type III may be represented more specifically by the constitution where M=bivalent metal R alkyl hydrocarbon residues R =hydrogen, alkyl or aryl hydrocarbon residues.

One of the preferred members of this group is the zinc salt formed from a mixture 3 of one mol of dimethyl dithio carbamic acid and one mol of acetic acid. The chemical constitution of this zinc salt is thought probably to be Other combinations which are members of this group are given in the folowlng table.

Carbox ylic acid Dithio carbamic acid Metal Probable formula Dimethyl Dimetbyl Dimethyl Dimethyl Dimethyl Dimethyl Dimethyl Dimethyl Diethyl Dibutyl Stearic Benzoic Stearic Abietic Oleic Abietic Acetic Benzoic Steuric Benzoic Zinc Zinc Lead Lead Lead Zinc Lead Lead Lead Zinc There are many other materials of this type which function in this manner and the above examples serve only as an indication of the scope of the invention.

Example 5 The use of accelerators of Type III is illustrated in this example. The rubber stock as employed had the following composition:

In the following table giving tensile 0 strength values the accelerators employed are as follows:

Stock A: Zinc salt formed from one dimethyl dithio carbamic acid and one acetic acid.

molmol Probable formula: (CHa)2 N CSS-Zn-OOC-IJH;

mol mol Stock B: Zinc salt formed from one dimethyl dithio carbamic acid and one benzoic acid.

Probable formula: (CH3): NCSS' ZIPOOOCflHfi mol mol Stock C: Lead salt formed from one dimethyl dithio carbamic acid and one acetic acid.

Probable formula. oHm NCSS-Pb-OOQCH;

mol mol Stock D: Zinc salt formed from one dimethyl dithio carbamic acid and one stearic acid.

Probable formula: (CH3): NCsSZIl-OOC(CH2)ld-Cfi3 The above stocks were mixed and cured and the tensile strengths determined. These are given in the following table.

The tensile strengths are measured on a slab of rubber th of an inch in thickness StockA StockB StockC StockD Cure Q a o 7 a I i=3 E, E, g," E g 8 5 5 2 a: 2 a e a m a m- 1! 3' 4' 5' 150 7/ 8! 10' 350 2290 960% 15' 1160 820% 2390 900% 3g: 2140 900% 3480 930% 30 2450 860% 3450 900% 40 3365 870% 50 2990 830% 3170 850% 2O 3365 780 90 X203? 3585 750 120x20# 33-19 740% Type I V Where, in the formula R1MRI R; is a radical containing the mercapto SH) group.

The materials of Type IV may be represented more specifically by the constitution (Ra)aNCSSMS-Rb where,

M=bivalent metal Ra alkyl hydrocarbon residue Rb= alkyl, cyclic or heterocyclic hydrocarbon residues.

One of the preferred members of this group is the lead salt prepared from a molecular mixture of dimethyl dithio carbamic acid and mercaptobenzothiazole. This lead salt probably has the chemical constitution:

lead salt such as lead nitrate or lead acetate.

Other members of this group may be inand cured in a press. dicated as follows:

Metal Dithio carbamic acid Mercapto acid Probable formula N Zinc Dlmethyl Mercaptobenzothiazole (CHz)2NCSSZn-SO CuH;

. S-CH Zinc Dimethyl 4-1netby12-mercaptothiazole (CHQzNCSS-Zn-SO N-C-CHa I s-oH Lead Dimethyl 4-methyl 2-mercaptothiazole (CH:):NCSS--PbSO N-o-cn, P,

Metal Dithio carbamic acid Mercapto acid Probable formula Lead Diethyl Mercaptobenzothiazole (GgH5)zNCSS-Pb$0 /CuH4 Zinc Dibutyl Mercaptobenzothlazole (C4H9)zNCSS- ZI1-SC\ /C0H4 Zinc Diethyl Mercaptobenzothiazole (CzH5)zNCSS-ZDSC\ CH4 Lead Dibutyl Mercaptobenzothlazole (C4H9)2NCSSPb-SC CaH4 N-CH:

Lead Dimethyl Thiazoline 2-mercaptan (C Ha)2NCSSPbSO Zinc Dimethyl Ethyl mercaptan (CH3) NCSS-ZnSOzH Lead Dimethyl Phenyl mercaptan (CH 3)zNGSSPb-SC5H5 The above members serve to show the wide 7 Stock A Stock B range of compounds of Type IV. Cu

re T0 lllustrate the use of members of this Tensile Elong Tensile Elong type the following example is given.

Ewa/mple 6 The rubber compound used in this example consists of:

Rubber 100 Zinc oxide; 10 Sulphur 4 Accelerator 1 The accelerators used are:

Stock A: 1% lead salt from one mol dimethyl dithio carbamate and one mol mercaptobenzothiazole.

Probable formula: (CH3)2NCSSPbS-C\ /CH4 Stock B1 1% zinc salt from one mol dimethyl dithio carbamate and one mol mercaptobenzothiazole.

The above stocks were compounded and mixed and upon sheeting out were press:

Type V Where, in the formula, Rr-l.V.[-R:

R is an alkylidene-bis dithio carbamic acid radical derived from a primary alkyl or aryl amine.

The materials of this type may be repre- M ==bivalent metal Ra, Rb =alkyl hydrocarbon residues Re, Re =alkyl or aryl hydrocarbon residues =hydrogen, alkly or,aryl hydrocarbon residues.

One of the preferred members of this group may be termed methylene bis lead phenyl dimethyl dithio carba-mate the chemical constitution probably being:

This'material may be prepared by treating amixture of 394 grams (one mol) of sodium methylene bis phenyl dithio carbamate and 246 grams (twomols) of sodium dimethyl dithio carbamate with 650 grams (two mole) of lead acetate. The precipitated lead salt Y is then filtered, driedand pulverized and is ready for use.

Other members of this following:

Butylidene bis lead thio carbamate Ethylidene bis zinc phenyl dimethyl dithio carbamate Methylene bis zinc ortho tolyl dimethyl dithio carbamate group include the phenyl dimethyl di- Ethylidene his lead xylyl dimethyl dithio carbamate Methylene bis lead para tolyl dimethyl dithio carbamate Methylene bis zinc xylyl dimethyl dithio carbamate Methylene bis zinc beta naphthyl dimethyl dithio carbamate Ethylidene bis lead para tolyl dimethyl dithio carbamate Butylidene bis zine phenyl dimethyl 11- thio carbamate Methylene bis lead xylyl dimethyl dithio carbamate The above examples serve to indicate the wide scope of this type of accelerators.

Ewample 7 To illustrate the use of materials of Type V a rubber stock was compounded containing 0.65 parts of methylene bis lead phenyl dimethyl dithio carbamate The other ingredients are as follows:

Rubber 55.3125 Stearic acid 2.0 Sulphur 2.25 Carbon black 20.0 Zinc oxide 16.2875 Pine tar oil 3.5

The above stock was compounded, mixed and milled and upon curing, the tensile strengths were determined. The tensile strength was measured on slabs 'f cth of an inch in thickness and press-cured.

1. A rubber composition including a bivalent metallic salt containing two different acidic groups one of which is a dialkyl dithio carbamic acid group.

2. A rubber composition including a bivalent metallic salt made from two different acids, one of which is a dialkyldithio car- Y bamic acid.

3. A rubber composition including a bivalent metallic salt containing a dialkyl dithio-carbamic acid group and a dithio carbamic acid group derived from a cyclic amine.

4:. A rubber composition including a' bivalent metallic salt made from amixture'of two dithio carbamic acids, one of which is derived from adialkyl amine and the other from acyclic amine,

5. A rubber composition including a bi-v valent metallic salt .containinga dialkyl di-' thio carbamic acid group and ajdithio carbamic acid group derived from a straight chain aliphatic amine substituted by one or more cyclic groups.

6. A rubber composition including a bivalent metallic salt containing a dialkyl dithio carbamic acid group and a dithio carbamic acid group derived from an aliphatic diamine.

7. A rubber composition including a bi-- valent metallic salt containing a dialkyl dithio carbamic acid group and a dithio carbamic acid group derived from an aliphatic dianiine substituted residues.

8. A rubber composition including a bivalent metallic salt containing a dialkyl dithio carbamic acid group and a dithio carbamic acid group derived from a 1-2 di (aryl amido) ethane. I u

9. A rubber composition including a bivalent metallic salt containing a dialkyl dithio carbamic-acid group and a dithio carbamic by aryl hydrocarbon acid group derived from a substituted 1-2 di 1 aryl amido) ethane.

10. A rubber composition including a biva- I lent metallic salt made from a mixture of two dithio carbamic acids one of which is derived froma dialkyl dimethyl amine and the other from a straight chain aliphatic amine sub stituted by one or more cyclic groups.

11. A rubber composition including a bivalent metallic salt made from a mixture of two dithio carbamic acids one of which is derived from dimethyl amine and the other from an aliphatic diamine.

12. A rubber composition including a bivalent metallic salt made from a mixture of two dithio carbamic acids one of which is derived from dimethyl amine and the other from an aliphatic diamine substituted by aryl hydrocarbon residues.

13. A rubber composition including a bivalent metallic salt made from a mixture of two dithio carbamic acids one of which is derived from dimethyl amine and the other from a 12 di (aryl amido) ethane.

14. A rubber composition including a bivalent metallic salt made from a mixture of two dithio carbamic acids one of which is derived from dimethyl amine and the other from a substituted 12 di (aryl amido) ethane.

15. A rubber composition including the lead salt made from a mixture of dimethyl dithio carbamic acid and N (beta anilino ethyl) phenyl dithio carbamic acid.

16. A. rubber composition including the lead salt made from a mixture of dimethyl dithio carbamic acid and the dithio carbamic acid derived from 12 di (phenyl amino) ethane.

17. A rubber composition including lead [(beta anilino ethyl) phenyl] dimethyl dithio carbamate.

18 A rubber composition including a bivalent metallic salt wherein the metal has replaced the hydrogen atoms of two different organic compounds, one of which is a dialkyl dithio carbamic acid.

19. A rubber composition including a bivalent metallic salt wherein the metal has replaced the hydrogen atoms of the -SH groups of two difi'erent organic compounds,

' one "of which is a dialkyl dithio carbamic acid.

20. A rubber composition including a bivalent metallic salt wherein the metal has replaced the hydrogen atoms of two different organic compounds, both of which are dithio carbamic acids. i

21. A rubber composition including a bivalent metallic salt wherein the metal has replaced the hydrogen atoms of two different organic compounds, one of which is dimethyl dithio carbamic acid.

' .22. A rubber composition including a bivalent metallic salt wherein the metal has replaced the hydrogen atoms of the SH groups of two different organic compounds, one of which is dimethyl dithio carbamic acid.

2 3. A process for accelerating the vulcanization of a rubber compound, which comprises 

